Semiconductor laser devices, such as double heterostructure laser diodes, are utilized in various applications, such as for optical sources in fiber optic communications. In the manufacture of such devices, double heterostructures are grown and processed on a wafer substrate using, for example, liquid phase epitaxy techniques. The wafer is then cleaved into typically solid rectangular laser bars containing many laser diodes. The laser diodes are functional at the laser bar level, and therefore electrical/optical testing is often performed at this level prior to cleaving the individual laser diodes from the bars.
Each laser bar has two end faces, or facets, formed during the cleaving process. Laser light is ultimately transmitted through the facets, so it is important for their surfaces to remain unperturbed and uncontaminated during handling of the laser bar. Following the cleaving operation on the wafer to form the laser bars, the facets are coated with an optical coating in a facet coating apparatus. A known apparatus for retaining laser bars during the facet coating processes is a facet coat holding fixture. The fixture also transports the bar to and from the facet coating process.
A problem encountered due to the coating process is that often the optical coating deposits on not only the laser bars but also the fixtures used for retaining the laser bars. This may lead to laser bars sticking to the fixtures and to the fixtures becoming contaminated by the optical coating, eventually leading to sticking and gauging of the fixture.
If a laser bar remains adhered to a fixture, an additional operation is then required to detach the laser bar from the fixture. One example of such an additional operation includes manually shaking the fixture to loosen the laser bar. Another example is physically prying the laser bar from the fixture with a pick or other similar device. Such operations result in a reduction in the yield of usable laser bars, since a number of the laser bars become damaged when pried or shaken from the fixture blades. Typically, as many as half of the laser bars may become damaged from these additional operations.
A second problem is that during the coating process, the coating may creep in between the laser bars and the fixtures, becoming deposited on the p-and/or n-bonding sides of the laser bars. This is referred to as overspray. The p-and n-bonding sides of the laser bars include bonding pads formed of gold, or another suitable conductive material. Deposition of the coating on the p- and n-bonding sides may lead to partial covering of the bonding pads, thereby reducing the possible sites for bonding with a solder material. Excessive deposition may reduce the possible sites for bonding to such an extent as to prevent contact bonding or cause a contact bonded laser to fail.
Due to the inherent problems in conventional methodologies related to the coating process, there exists a need for an improved fixture and method for withstanding the effects of overspraying and sticking.